Abstract

The Magpie volcanogenic massive sulfide prospect is hosted within the Trooper Creek Formation of the Cambrian Seventy Mile Range Group in North Queensland, Australia. An original chlorite + or - quartz + or - sericite + or - sulfide alteration zone is interpreted to have formed as a result of Mg-Fe-K metasomatism associated with the formation of the mineralization. This assemblage has undergone low-pressure, medium- to high-temperature metamorphism by the nearby Ravenswood Granodiorite. The conditions of metamorphism were deduced as P = 1 to 3 kbars, T = 500 degrees to 600 degrees C, log f (sub O 2 ) = -16, and log f (sub O 2 ) = -1 to -2.The main sulfide-bearing mineralized horizon is characterized by an enrichment of Fe, MgO, and base metals, a depletion of CaO and Na 2 O, and is interpreted as being a hydrothermal exhalite of interlayered chert and sulfides. The stratigraphic footwall consists of highly altered rhyodacitic tuff and mafic volcanics and shows a strong depletion of CaO and Na 2 O and an enrichment of Fe, MgO, MnO, and base metals. The stratigraphic hanging wall is a series of rhyodacitic and rhyolitic tuffs and pyroclastics, which are characterized by silicification, sericitization, a depletion in Na 2 O, and an enrichment in Fe.

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